CN114835174A - Low-cobalt positive electrode active material, method for producing same, electrochemical device, and electronic device - Google Patents

Low-cobalt positive electrode active material, method for producing same, electrochemical device, and electronic device Download PDF

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CN114835174A
CN114835174A CN202210602467.8A CN202210602467A CN114835174A CN 114835174 A CN114835174 A CN 114835174A CN 202210602467 A CN202210602467 A CN 202210602467A CN 114835174 A CN114835174 A CN 114835174A
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cobalt
low
salt
equal
active material
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CN114835174B (en
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杨文龙
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Envision Power Technology Jiangsu Co Ltd
Envision Ruitai Power Technology Shanghai Co Ltd
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Envision Power Technology Jiangsu Co Ltd
Envision Ruitai Power Technology Shanghai Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/40—Nickelates
    • C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
    • C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
    • C01G53/50—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [MnO2]n-, e.g. Li(NixMn1-x)O2, Li(MyNixMn1-x-y)O2
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a low-cobalt positive electrode active material, a preparation method thereof, an electrochemical device and electronic equipment, wherein the preparation method comprises the following steps: (1) mixing nickel salt, cobalt salt, manganese salt, a complexing agent and a precipitator, and carrying out coprecipitation reaction to obtain a precursor core; (2) increasing the molar concentration of the cobalt salt, reducing the molar concentration of the manganese salt, and carrying out coprecipitation reaction to obtain a low-cobalt precursor; (3) mixing the low-cobalt precursor with lithium salt, and sintering to obtain the low-cobalt positive electrode active material; the molar concentration ratio of the nickel salt, the cobalt salt and the manganese salt in the step (1) is x: y (1-x-y), wherein x is more than or equal to 0.55 and less than or equal to 0.60, and y is more than or equal to 0.05 and less than or equal to 0.15. The invention overcomes the defects of low capacity and poor storage caused by sintering cladding cobalt by a pyrogenic process, improves the crystallinity, interface stability and dynamic performance of the material, and further improves the gram capacity, coulombic efficiency and capacity retention rate of the electrochemical device.

Description

Low-cobalt positive electrode active material, method for producing same, electrochemical device, and electronic device
Technical Field
The invention belongs to the technical field of batteries, and relates to a low-cobalt positive electrode active material, a preparation method thereof, an electrochemical device and electronic equipment.
Background
The ternary material has higher theoretical specific capacity and voltage platform, but the cost of cobalt in the ternary material is higher, and the product cost can be saved by reducing the content of cobalt; however, the decrease of the cobalt content in the ternary material affects the overall conductivity of the material, and increases the diffusion barrier of lithium ions in crystal lattices, so that the reaction kinetics of the material is delayed, and the capacity exertion of the material is finally affected.
At present, when a low-cobalt ternary material is sintered by a pyrogenic process, the problem of dynamics of the material can be solved by coating cobalt on the surface of the low-cobalt ternary material, but the cobalt can be effectively coated only when the temperature of secondary sintering is 700-800 ℃, but other coating elements can migrate and permeate into the material particles at the temperature, so that the coating effect is influenced, and the high-temperature storage performance of the material is deteriorated; therefore, the preparation method of the low-cobalt ternary material with excellent dynamic performance is provided, and the preparation method has important significance for reducing the production cost and improving the performance of the low-cobalt ternary material.
Disclosure of Invention
In view of the defects in the prior art, the invention aims to provide a low-cobalt positive electrode active material, a preparation method thereof, an electrochemical device and electronic equipment. According to the invention, the concentration of the metal salt is controlled, two-step coprecipitation reaction is carried out, so that the low-cobalt cathode active material with low cobalt inside and rich cobalt on the surface is obtained, the defects of low capacity and poor storage caused by sintering and coating cobalt by a pyrogenic process are overcome, and the prepared material has the advantages of uniform particles, good sphericity, narrow particle size distribution, higher crystallinity and interface stability, excellent dynamic performance and higher gram capacity, coulombic efficiency and capacity retention rate when applied to an electrochemical device.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a low-cobalt cathode active material, the method comprising the steps of:
(1) mixing nickel salt, cobalt salt, manganese salt, a complexing agent and a precipitator, and carrying out coprecipitation reaction to obtain a precursor core;
(2) increasing the molar concentration of the cobalt salt, reducing the molar concentration of the manganese salt, and carrying out coprecipitation reaction to obtain a low-cobalt precursor;
(3) mixing the low-cobalt precursor with lithium salt, and sintering to obtain the low-cobalt positive electrode active material;
the molar concentration ratio of the nickel salt, the cobalt salt and the manganese salt in the step (1) is x: y (1-x-y), wherein x is more than or equal to 0.55 and less than or equal to 0.60, and y is more than or equal to 0.05 and less than or equal to 0.15.
In the present invention, the low-cobalt positive electrode active material refers to a material having a chemical formula of LiNi x Co y Mn 1-x-y O 2 Y is not more than 0.15.
In the invention, the molar concentration ratio of the nickel salt, the cobalt salt and the manganese salt in the step (1) is x: y (1-x-y), wherein x is more than or equal to 0.55 and less than or equal to 0.60, such as 0.55, 0.56, 0.57, 0.58, 0.59 or 0.6, etc., and y is more than or equal to 0.05 and less than or equal to 0.15, such as 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14 or 0.15, etc. Within the element proportion range, the safety of the finished battery can be improved, and the use of rare cobalt element can be reduced.
According to the method, nickel salt, cobalt salt, manganese salt, a complexing agent and a precipitating agent with certain concentrations are mixed for coprecipitation reaction, after a precursor core is generated, the concentrations of the cobalt salt and the manganese salt in a container of the coprecipitation reaction are changed for coprecipitation, a cobalt-rich coating layer is formed on the surface of the precursor core by increasing the concentration of the cobalt salt and reducing the concentration of the manganese salt, a low-cobalt precursor is obtained, and finally, lithium salt is added for sintering to obtain the low-cobalt cathode active material with low cobalt inside and rich cobalt on the surface.
According to the preparation method, the concentration of metal salt is controlled only in the wet process stage without fire sintering coating, materials with different contents of cobalt inside and outside are generated through two coprecipitation reactions, the prepared low-cobalt precursor is uniform in particle, good in sphericity and narrow in particle size distribution, the low-cobalt positive active material is obtained through sintering of the low-cobalt precursor and lithium salt, the crystallinity and the interface stability of the low-cobalt positive active material are controlled within the optimal range, the polarization of an electrochemical device is reduced, the dynamic performance of the electrochemical device is improved, and therefore the electrochemical device with excellent capacity, circulation, storage and other performances is obtained.
It should be noted that, in the present invention, a manner of increasing the molar concentration of the cobalt salt and decreasing the molar concentration of the manganese salt is not specifically limited, for example, the coprecipitation reaction in step (1) and step (2) is performed in two reaction kettles, the precursor core in step (1) is taken out of the reaction kettle and placed in another reaction kettle, and nickel salt, manganese salt, cobalt salt, complexing agent and precipitant are added and mixed, at this time, the molar concentration of the added cobalt salt is higher than that in step (1), and the molar concentration of the added manganese salt is lower than that in step (1), and then the coprecipitation reaction is performed, so as to obtain the low-cobalt precursor.
Preferably, the volume ratio of the precursor core to the low cobalt precursor is 1 (1.5 to 2.5), and may be, for example, 1:1.5, 1:1.8, 1:2, 1:2.2, or 1:2.5, etc.
The method preferably changes the concentration of the metal salt when the volume of the precursor core grows to about half of the volume of the low-cobalt precursor, sets different reaction stages according to different particle sizes, and further increases the preparation cost of the material when the volume of the precursor core is larger, and the cobalt content is higher; when the precursor volume is smaller, the capacity, dynamics and cycle performance of the material are affected.
In the present invention, the low cobalt precursor and the precursor core have a high sphericity and a spherical or spheroidal shape, and in the case of a spherical shape, when the volume ratio of the precursor core to the low cobalt precursor is 1:2, that is, the radius of the precursor core is equal to the radius of the low cobalt precursor (1/2) 1/3 。
Preferably, the nickel salt of step (1) comprises nickel sulfate.
Preferably, the manganese salt of step (1) comprises manganese sulfate.
Preferably, the cobalt salt of step (1) comprises cobalt sulfate.
Preferably, the complexing agent of step (1) comprises ammonia.
Preferably, the precipitant of step (1) comprises sodium hydroxide.
It should be noted that, in the present invention, the molar concentrations of the complexing agent and the precipitating agent are not particularly limited, and the contents thereof may meet the precipitation requirement, and for example, the molar concentration of the complexing agent may be 1mol/L to 3mol/L, and the molar concentration of the precipitating agent may be 6mol/L to 12 mol/L.
Preferably, in the step (2), the molar concentration of the cobalt salt is increased, and after the molar concentration of the manganese salt is reduced, the molar concentration ratio of the nickel salt, the cobalt salt and the manganese salt is x: z (1-x-z), wherein y is more than or equal to 0.05 and less than or equal to z and less than or equal to 0.15, and z can be 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14 or 0.15, and the like.
As a preferred technical scheme of the preparation method, y is more than or equal to 0.05 and less than or equal to 0.1, z is more than or equal to 0.1 and less than or equal to 0.15, and further preferably, y is more than or equal to 0.09 and less than or equal to 0.1, and z is more than or equal to 0.14 and less than or equal to 0.15.
According to the invention, the content of the cobalt element in the inner core and the shell is further optimized, so that the cost of the NCM ternary material can be reduced, the capacity can be ensured to be exerted while the cost is reduced, and the dynamics and the cycle performance are improved; different from the pyrometallurgical sintering coating, the invention coats the end of the precursor with cobalt with proper content to improve the defect of low capacity of the pyrometallurgical method.
Preferably, after the coprecipitation reaction in step (2) and before the sintering in step (3), the operations of washing, drying, mixing, sieving, demagnetizing and packaging the low-cobalt precursor are further included.
Preferably, the molar ratio of the low-cobalt precursor and the lithium salt in the step (3) is 1 (1.04 to 1.06), and may be, for example, 1:1.04, 1:1.045, 1:1.05, 1:1.055, 1:1.06, or the like.
Preferably, the sintering temperature in step (3) is 900 ℃ to 1000 ℃, and may be 900 ℃, 920 ℃, 940 ℃, 960 ℃, 980 ℃, or 1000 ℃, for example.
Preferably, the sintering time in step (3) is 10h to 20h, for example, 10h, 12h, 14h, 16h, 18h or 20h, etc.
In a second aspect, the invention provides a low-cobalt positive electrode active material, which is prepared by the preparation method according to the first aspect, and comprises a low-cobalt positive electrode active material core and a low-cobalt positive electrode active material shell coated on the surface of the low-cobalt positive electrode active material core;
the low cobalt positive electrode active material core comprises LiNi x Co y Mn 1-x-y O 2 The low-cobalt positive active material shell comprises LiNi x Co z Mn 1-x-z O 2 Wherein x is more than or equal to 0.55 and less than or equal to 0.60, and y is more than or equal to 0.05 and less than or equal to 0.60<z≤0.15。
According to the invention, the low-cobalt cathode active material is in a core-shell structure, the core is a low-cobalt component, and the shell is a cobalt-rich component, so that the lithium ion diffusion rate of the single-component low-cobalt material is improved, the polarization and the internal resistance of the material are greatly reduced, and the gram capacity, the coulombic efficiency and the cycle performance of the material are improved.
Preferably, the total molar amount of cobalt in the low cobalt positive electrode active material is 5% to 15%, for example, may be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or the like, based on 100% of the total molar amount of nickel, cobalt, and manganese in the low cobalt positive electrode active material. On one hand, compared with the surface cobalt-rich cathode active material with the cobalt content increasing linearly from the inner core to the outer shell, on the other hand, the cobalt-rich region of the low-cobalt cathode active material is thicker and the polarization is lower during lithium removal, while the cobalt content of the cathode active material is increased linearly and the cobalt-rich region is thinner, so that the polarization is higher; on the other hand, in consideration of the preparation method, the low-cobalt cathode active material only needs to change the concentration of the metal salt once, the controllability is strong, the size and the shape of the target product are easy to adjust, and if the linear increasing or decreasing of the cobalt content of the cathode active material is realized, the concentration of the cobalt salt is required to be changed step by step, the cathode active material is easy to reach a larger size when the target product is not generated, or the target product cannot be generated when the target size is reached, so that the generation of the low-cobalt cathode active material with proper size and shape is influenced, and the electrochemical performance of the material is reduced.
Preferably, the surface of the low-cobalt positive electrode active material comprises free lithium, and the content of lithium element in the free lithium is 150ppm to 1000ppm based on the mass of the low-cobalt positive electrode active material, and may be 150ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm or the like, for example.
In a third aspect, the present invention provides an electrochemical device comprising a low cobalt positive electrode active material according to the second aspect in a positive electrode thereof.
The low-cobalt positive electrode active material has high crystallinity, stable low-cobalt interface structure, small polarization, small internal resistance and good dynamic performance, and an electrochemical device prepared by the low-cobalt positive electrode active material has higher gram capacity, coulombic efficiency and circulating capacity retention rate.
In an alternative embodiment, the present invention provides a method for detecting whether a low cobalt positive active material according to the present invention is contained in an electrochemical device, comprising:
splitting the sample of the electrochemical device to obtain a positive electrode, washing and drying the positive electrode by adopting a solvent, blade-coating the surface of the positive electrode to obtain active substance powder, carrying out an Inductively Coupled Plasma (ICP) test on the active substance powder or cutting the particle section of the active substance powder by using a focused ion beam, and matching with an EDS line scanning or surface scanning test to obtain the distribution condition and the content of each element;
when the test result shows that the particles in the active material powder are divided into the inner core and the coating layer, the inner core and the coating layer both contain Ni, Co and Mn, the cobalt content inside and outside the particles has an obvious boundary, and the cobalt content in the inner core is lower than that in the coating layer, so that the positive electrode of the electrochemical device sample can be confirmed to contain the low-cobalt positive electrode active material.
In an alternative embodiment, the present invention provides a method for preparing the positive electrode, including:
and mixing the low-cobalt positive electrode active material, the conductive agent, the binder and the solvent to obtain positive electrode slurry, coating the positive electrode slurry on an aluminum foil, and rolling to obtain the positive electrode.
Preferably, the conductive agent includes conductive carbon black (SP) and/or Carbon Nanotubes (CNT).
Preferably, the binder comprises polyvinylidene fluoride (PVDF).
Preferably, the mass ratio of the low-cobalt cathode active material, the SP, the CNT and the PVDF is (90 to 99):1:0.5:1, and may be, for example, 90:1:0.5:1, 92:1:0.5:1, 94:1:0.5:1, 96:1:0.5:1, 98:1:0.5:1 or 99:1:0.5:1, etc.
In an alternative embodiment, the electrochemical device is a lithium ion battery.
In an alternative embodiment, the negative electrode of the electrochemical device comprises graphite, SP, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of (90 to 99):1:1.5:2, for example, 90:1:1.5:2, 92:1:1.5:2, 94:1:1.5:2, 96:1:1.5:2, 98:1:1.5:2 or 99:1:1.5:2, etc.
In an alternative embodiment, the electrolyte of the electrochemical device includes a lithium salt and a solvent.
In an alternative embodiment, the lithium salt comprises LiPF 6 。
In an alternative embodiment, the lithium salt is present in an amount of 4 wt% to 24 wt%, for example 4 wt%, 8 wt%, 10 wt%, 15 wt%, 20 wt%, or 24 wt%, etc., based on 100 wt% of the mass of the electrolyte.
In an alternative embodiment, the solvent comprises at least one of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC), dimethyl carbonate (DMC) and Polycarbonate (PC) or a combination of any two thereof, for example, a combination of EC and EMC, a combination of DMC and PC, a combination of EC, EMC and DMC, or a combination of EC, EMC, DMC and PC, or the like.
In an alternative embodiment, the mass ratio of EC, EMC, DMC and PC in the solvent is (2 to 4): (3 to 5): (2 to 4): (0 to 1), the selection range of EC (2 to 4) may be, for example, 2, 2.5, 3, 3.5, or 4, etc., the selection range of EMC (3 to 5) may be, for example, 3, 3.5, 4, 4.5, or 5, etc., the selection range of DMC (2 to 4) may be, for example, 2, 2.5, 3, 3.5, or 4, etc., the selection range of PC (0 to 1) may be, for example, 0, 0.1, 0.2, 0.3, 0.5, 0.7, or 1, etc., and when PC is 0, it means that PC is not contained in the solvent.
In an alternative embodiment, the separator of the electrochemical device has a thickness of 9 μm to 18 μm, and may be, for example, 9 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, or the like.
In an alternative embodiment, the separator of the electrochemical device has an air permeability of 180s/100mL to 380s/100mL, and may be, for example, 180s/100mL, 200s/100mL, 240s/100mL, 250s/100mL, 280s/100mL, 300s/100mL, 250s/100mL, or 380s/100mL, or the like.
In an alternative embodiment, the separator of the electrochemical device has a porosity of 30% to 50%, for example, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or the like.
In the present invention, a method of assembling an electrochemical device using the cathode, the anode and the separator is the prior art, and those skilled in the art can assemble the electrochemical device by referring to the method disclosed in the prior art. Taking a lithium ion battery as an example, a positive electrode, a diaphragm and a negative electrode are sequentially wound or stacked to form a battery core, the battery core is placed in a battery case, electrolyte is injected, formation and packaging are performed, and the electrochemical device is obtained.
The diaphragm with appropriate parameters is selected to be matched with the anode and the cathode to prepare the electrochemical device, so that the capacity and the cycling stability of the electrochemical device are improved.
In a fourth aspect, the invention provides an electronic device comprising an electrochemical device according to the third aspect.
The electronic device according to the present invention may be, for example, a mobile computer, a portable phone, a memory card, a liquid crystal television, an automobile, a motorcycle, a motor, a timepiece, a camera, or the like.
Compared with the prior art, the invention has the beneficial effects that:
according to the preparation method, the concentration of metal salt is controlled only in the wet process stage without fire sintering coating, materials with different contents of cobalt inside and outside are generated through two coprecipitation reactions, the prepared low-cobalt precursor is uniform in particle, good in sphericity and narrow in particle size distribution, the low-cobalt positive active material is obtained through sintering of the low-cobalt precursor and lithium salt, the crystallinity and the interface stability of the low-cobalt positive active material are controlled within the optimal range, the polarization of an electrochemical device is reduced, the dynamic performance of the electrochemical device is improved, and therefore the electrochemical device with excellent capacity, circulation, storage and other performances is obtained.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments.
Example 1
The embodiment provides a preparation method of a low-cobalt positive electrode active material, which comprises the following steps:
(1) adding nickel sulfate, cobalt sulfate, manganese sulfate, ammonia water and sodium hydroxide into a reaction kettle, carrying out coprecipitation reaction, stopping the reaction when the volume of the product of the coprecipitation reaction is half of the volume of the target product, and obtaining precursor kernel Ni 58 Co 10 Mn 32 (OH) 2 ；
(2) Taking out the precursor core in the step (1), mixing the precursor core with nickel sulfate, cobalt sulfate, manganese sulfate, ammonia water and sodium hydroxide in another reaction kettle, carrying out coprecipitation reaction again, and reacting on Ni 58 Co 10 Mn 32 (OH) 2 Surface formation of Ni 58 Co 12 Mn 30 (OH) 2 Obtaining a low-cobalt precursor, wherein the volume of the low-cobalt precursor is 2 times of the volume of the inner core of the precursor;
(3) mixing the low-cobalt precursor in the step (2) with lithium hydroxide according to a molar ratio of 1:1.05, and sintering at 950 ℃ for 17 hours to obtain a low-cobalt cathode active material;
wherein the molar concentration ratio of nickel sulfate, cobalt sulfate and manganese sulfate in the reaction kettle in the step (1) is 0.58:0.1:0.32, and the molar concentration ratio of nickel sulfate, cobalt sulfate and manganese sulfate in the reaction kettle in the step (2) is 0.58:0.12: 0.3.
The low-cobalt positive active material prepared in this example includes a low-cobalt positive active material inner core LiNi 0.58 Co 0.1 Mn 0.32 O 2 And a low-cobalt positive electrode active material shell LiNi coated on the surface of the inner core of the low-cobalt positive electrode active material 0.58 Co 0.12 Mn 0.3 O 2 The surface of the low-cobalt positive electrode active material also comprises free lithium, and the content of lithium element in the free lithium is 338ppm by taking the mass of the low-cobalt positive electrode active material as a reference.
Assembling of lithium ion battery
(1) Preparation of the positive electrode: mixing the low-cobalt positive electrode active material prepared in the embodiment and the comparative example, SP, CNT and PVDF with N-methyl pyrrolidone (NMP) according to the mass ratio of 97.5:1:0.5:1 to prepare positive electrode slurry, coating the positive electrode slurry on an aluminum foil, and rolling to obtain a positive electrode;
(2) preparation of a negative electrode: mixing graphite, SP, CMC and SBR according to a mass ratio of 95.5:1:1.5:2 to prepare slurry, coating the slurry on a copper foil, and rolling to obtain a negative electrode;
(3) preparing a lithium ion battery: adhering an aluminum positive electrode tab to a positive electrode, adhering a copper negative electrode tab to a negative electrode, selecting a diaphragm with the thickness of 10 μm, the air permeability of 200s/100mL and the porosity of 40%, sequentially and tightly overlapping the positive electrode, the diaphragm and the negative electrode, and injecting 5 wt% LiPF solute into two sides of the diaphragm 6 And the solvent is an electrolyte of EC, EMC, DMC and PC with the mass ratio of 3:4:3:0.5 to obtain the battery cell, and the battery cell is stacked to the required number of layers to obtain the lithium ion battery.
Second, performance test
(1) Testing of low-cobalt positive electrode active material:
the method for testing the cobalt element in the low-cobalt positive electrode active material comprises the following steps: cutting the powder particles by using a focused ion beam method, and then testing the distribution condition of the cobalt element by using a time-of-flight secondary ion mass spectrometer.
Testing the content of free lithium on the surface of the low-cobalt positive electrode active material: 1g of low-cobalt positive electrode active material powder is placed in deionized water, stirred by a glass rod for 5 minutes and kept stand for 4 hours, then supernatant is taken, and LiOH and Li are tested by a potentiometric titrator 2 CO 3 The content of (a), wherein the amount of lithium element, is the content of surface-coated free lithium.
(2) Testing of the lithium ion battery:
adopting a battery performance test system (equipment model: BTS05/10C8D-HP) of the Shenghong electric appliance component electric company Limited to carry out a first discharge capacity test and a 800-week circulation capacity retention rate test;
the first discharge gram capacity test method comprises the following steps: under the condition of 25 ℃, charging and discharging for one week in a charging and discharging mode of 0.063A/g, wherein the voltage interval is 2.8V to 4.35V, and the obtained charging and discharging capacity is divided by the usage amount of a positive electrode, namely the first charging/discharging gram capacity; the first coulombic efficiency is obtained by dividing the first discharge capacity by the first charge capacity.
Circulation capacity retention test method: cycling is carried out under the condition of 25 ℃ in a charging and discharging mode of 0.19A/g (calculated by the mass of the anode material), and the voltage interval is 2.8V to 4.35V. After the cycle time reaches 800 weeks, the discharge capacity of the battery at the moment is divided by the discharge capacity of the first cycle, and the cycle capacity retention rate of the battery at 800 cycles is obtained.
Examples 2 to 7 and comparative examples 1 to 2 were modified based on the procedure of example 1, and the specific modified parameters and test results are shown in tables 1 to 4.
TABLE 1
Figure BDA0003669854080000111
TABLE 2
Figure BDA0003669854080000112
As can be seen from comparison between the example 1 and the examples 4 to 5 in the table 2, when the volume ratio of the precursor core to the low-cobalt precursor is 1 (1.5 to 2.5), the prepared material has lower cost and the best electrochemical performance; in the embodiment 4, the precursor inner core is larger, the inner core of the prepared low-cobalt cathode active material is larger than the shell, the preparation cost of the product is increased, and the capacity and the cycle performance of the material are not obviously improved; in example 5, the precursor core is smaller, the prepared low-cobalt cathode active material has smaller core and more shell, and the capacity, the dynamic performance and the cycle performance of the material are affected, so that in example 1, the first-time discharge gram capacity, the coulombic efficiency and the 800-week cycle capacity retention rate of the prepared low-cobalt cathode active material are the best by adopting a proper volume ratio of the precursor core to the low-cobalt precursor.
TABLE 3
Figure BDA0003669854080000121
As can be seen from comparison between example 1 and examples 6 to 7 in table 3, in the present invention, by adjusting the metal salt concentration during the co-precipitation in step (1) and step (2), the outer shell and the inner core in the low-cobalt positive electrode active material have specific cobalt content, and the inner core and the outer shell are matched, so as to further improve the gram volume, coulombic efficiency, and capacity retention ratio of the material. The cobalt contents of the outer shell and the inner core of the low-cobalt cathode active material prepared in example 1 were in the optimum range, and thus, the capacity and cycle stability of example 1 were higher than those of examples 6 to 7.
Comparative example 1
The operation of the step (2) is eliminated, and after the sintering in the step (3), the sintered product is mixed with LiNi 58 Co 12 Mn 30 O 2 Mixing and sintering at 650 ℃ for 6h, all the other steps being the same as in example 1.
Comparative example 2
The procedure of example 1 was repeated except that the operation of step (2) was not conducted.
TABLE 4
Figure BDA0003669854080000122
As can be seen from comparison between example 1 and comparative examples 1 to 2 in table 4, the first discharge capacity, the coulombic efficiency, and the cycle capacity retention rate of the low-cobalt cathode active material produced by firing or by co-precipitation only in one step are all affected. In the comparative example 1, a layer of cobalt-rich material is directly sintered on the surface of the precursor core obtained by precipitation, and in the comparative example 2, secondary coprecipitation is not carried out, so that the structure with the cobalt-rich surface is not provided, and the electrochemical performance is obviously inferior to that of the embodiment 1.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A preparation method of a low-cobalt positive electrode active material is characterized by comprising the following steps of:
(1) mixing nickel salt, cobalt salt, manganese salt, a complexing agent and a precipitator, and carrying out coprecipitation reaction to obtain a precursor core;
(2) increasing the molar concentration of the cobalt salt, reducing the molar concentration of the manganese salt, and carrying out coprecipitation reaction to obtain a low-cobalt precursor;
(3) mixing the low-cobalt precursor with lithium salt, and sintering to obtain the low-cobalt positive electrode active material;
the molar concentration ratio of the nickel salt, the cobalt salt and the manganese salt in the step (1) is x: y (1-x-y), wherein x is more than or equal to 0.55 and less than or equal to 0.60, and y is more than or equal to 0.05 and less than or equal to 0.15.
2. The method of claim 1, wherein the volume ratio of the precursor core to the low-cobalt precursor is 1 (1.5-2.5).
3. The production method according to claim 1, wherein the nickel salt, manganese salt, cobalt salt, complexing agent and precipitating agent of step (1) satisfy any one of the following conditions (a) to (e):
(a) the nickel salt comprises nickel sulfate;
(b) the manganese salt comprises manganese sulfate;
(c) the cobalt salt comprises cobalt sulfate;
(d) the complexing agent comprises ammonia water;
(e) the precipitant comprises sodium hydroxide.
4. The method according to claim 1, wherein in the step (2), the molar concentration of the cobalt salt is increased, and the molar concentration of the manganese salt is decreased, the ratio of the molar concentrations of the nickel salt, the cobalt salt and the manganese salt is x: z (1-x-z), wherein y is greater than or equal to 0.05 and less than z is less than or equal to 0.15.
5. The production method according to claim 4, wherein the cobalt salt and the manganese salt satisfy any one of the following conditions (f) to (g):
(f) y is more than or equal to 0.05 and less than or equal to 0.1, and z is more than or equal to 0.1 and less than or equal to 0.15;
(g) y is more than or equal to 0.09 and less than or equal to 0.1, and z is more than or equal to 0.14 and less than or equal to 0.15.
6. The production method according to claim 1, wherein step (3) satisfies any one of the following conditions (h) to (i):
(h) the molar ratio of the low-cobalt precursor to the lithium salt is 1 (1.04-1.06);
(i) the sintering temperature is 900-1000 ℃;
(j) the sintering time is 10-20 h.
7. A low-cobalt positive electrode active material is prepared by the preparation method according to any one of claims 1 to 6, and comprises a low-cobalt positive electrode active material core and a low-cobalt positive electrode active material shell coated on the surface of the low-cobalt positive electrode active material core;
the low cobalt positive electrode active material core comprises LiNi x Co y Mn 1-x-y O 2 The low-cobalt positive active material shell comprises LiNi x Co z Mn 1-x-z O 2 Wherein x is more than or equal to 0.55 and less than or equal to 0.60, and y is more than or equal to 0.05 and less than or equal to 0.60<z≤0.15。
8. The low cobalt positive electrode active material according to claim 7, wherein a surface of the low cobalt positive electrode active material comprises free lithium, and a content of lithium element in the free lithium is 150ppm to 1000ppm based on a mass of the low cobalt positive electrode active material.
9. An electrochemical device comprising the low cobalt positive electrode active material according to claim 7 or 8 in a positive electrode thereof.
10. An electronic device, characterized in that the electrochemical device according to claim 9 is included in the electronic device.
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